Soft x-ray emission from Ar clusters irradiated by intense 150 fs laser pulses a t an intensity of～5×1015 W/cm2 has been measured with a flat field spe ctrometer. Strong transitions from ArⅧ charge states have been observed, some s pectral lines belong to ArⅫ and ArⅩⅢ. Compared with optical field ionization, the interaction of intense laser pulse with clusters enhances drastically the a bsorption of laser energy and higher charge states are obtained as well. The sig nificant change in the spectrum is attributed to the collisinal heating of small -sized Ar clusters formed at on enough baking pressure of gas.